1. Field of the Invention
The present invention relates to an asymmetrical resistant hinge set and particularly to an asymmetrical hinge set adopted for use on a support rack of portable electronic devices to anchor on a selected flipping angle without drifting.
2. Description of the Prior Art
Progress of computers has evolved from housed in a machine room to personal and notebook computers, and now to become touch control portable electronic device 1 (referring to FIG. 1) such as smart phones, tablet computers or the like. Users can directly and intuitively tap a computer screen 10 to select desired items, and splay or narrow two or more fingers to zoom graphics or texts on the screen larger or smaller. Such an operation approach shortens the distance between a user and screen 10 and is much user-friendly than the conventional computer which is operated through a keyboard interposed between the user and screen. The portable electronic device 1, with one set of touch screen as an operation interface, allows users to move freely on the screen 10 when in use. Usability improves greatly.
When a larger portable electronic device 1, such as a tablet computer, in use a user has to hold the computer with one hand and operate with another hand; even if it is rested on a desk or user's lap user still has to hold the display screen in an upright position with a palm at an optimal viewing angle. It's troublesome and easily causes fatigue on user's arm when used in a prolonged duration.
To remedy the aforesaid disadvantage, Applicant has proposed a support rack 2 for portable electronic devices (Taiwan patent No. 99205897, referring to FIGS. 2 and 3). It comprises a bumper 21, a support lid 22 and a hinge set 23. The hinge set 23 consists of two hinges 230. Each hinge 230 comprises an anchor seat 231, an anchor slider 232, a moving slider 233, a spring 234, a pintle 235 and a nut 236. The structure formed by the aforesaid elements can resolve the conventional problem. However it still has room for improvement. As the electronic device braced by the support rack, after coupling with the screen and circuitry, becomes heavier and is subject to a greater gravitational force, especially when the inclined angle is smaller approaching to the horizontal position. The hinge set 23 has to bear a heavier load. On the other hand, the electronic device equipped with the touch screen offers most smooth virtual keyboard entry operation when the inclined angle approximates to the horizontal position. But the spring 234 of the hinge set 23 does not have an adequate elastic force to bear the load, hence the support angle tends to drift. Choosing the spring or an elastic reed of a greater elastic force increases the resistance of the hinge 230 and a greater force is needed to flip the support lid 22, flipping operation is more difficult.